This invention relates to a magnetic recording medium, a magnetic head and a magnetic recording apparatus using the medium and the head, and particularly to a magnetic recording medium and a magnetic head having a protective film with a good durability on their respective surfaces and a highly reliable magnetic recording apparatus using the medium and the head.
Magnetic disks are applied to many fields of information memory and reproduction apparatuses of large capacity. All of these magnetic disks are required to have an increased recording capacity and a reliability that can withstand prolonged operations. A magnetic fields requiring a high recording density. However, magnetic recording density is applied particularly to disks requiring a high recording density. However, in case of the thin film magnetic medium type, an increase in the memory capacity inevitably makes sliding conditions severer, for example, a narrower clearance between the head and the disk, the resulting higher probability of contact sliding, etc. Thus, an increase in the sliding durability is indispensable. No magnetic disks of thin film magnetic medium type having a sufficient durability have been produced up to now.
One procedure now available to improve the durability is to decrease the friction and wearing during the sliding by use of a lubricant. It has been proposed to coat the surface of a magnetic disk only with a fluorine-based lubricant having a distinguished lubricating ability (Krytox 143, trademark of a product made by E.I. DuPont; Homblin Y, trademark of a product made by Monte-Fluous), as disclosed in U.S. Pat. Nos. 3,490,946 and 3,778,308. This procedure is very effective at the initial stage. However, when such a disk is used for a long time, the lubricant is gradually peeled off from the disk surface to decrease the lubricating effect, because the disk turns at a high speed.
It has been also proposed to coat the surface of a magnetic disk with a fluorine-based surfactant having a high adsorptivity, as disclosed in Japanese Patent Application Kokai (Laid-open) Nos. 59-116931, 58-41431, 58-29147, 57-154619 and 57-44226. Furthermore, it has been also proposed to chemically fix a fluorine-based lubricant to the surface of a magnetic disk as disclosed in U.S. Pat. No. 4,120,995 and Japanese Patent Application Kokai (Laid-open) Nos. 54-36171, 59-20323, 60-38730, 59-172159 and 61-39919.
Such fluorine-based surfactants and lubricants include compounds represented by the following general formula: EQU C.sub.n F.sub.2n+1 -SiZ.sub.3
wherein n=4 to 13 and X is a halogen atom, a nitrile group or an alkoxy group, and phosphoric acid-based compounds represented by the following general formula: EQU R.sub.f --P(O)--(OR).sub.m
wherein R.sub.f is a perfluoroalkyl group, R is C.sub.Z H.sub.2Z+1, m is 2 to 3 and Z is 0 to 3, as disclosed in Japanese Patent Application Kokai (Laid-open) Nos. 60-109028, 60-101717 and 60-246020. These lubricants are of such a type that the lubricants are fixed to a metal film or an oxide film on the surface of a disk by reaction therewith.
In the coating of the surface of a magnetic disk with the fluorine-based surfactants represented by the foregoing general formalae, the fluorine-based surfactants are not strongly fixed to the surface of the disk, and the surfactants are readily disengaged from the sliding surface during the sliding operation. Thus, the durability of a magnetic disk is not satisfactorily improved and also the durability of a recording apparatus is not improved.
In the procedures disclosed in U.S. Pat. No. 4,120,995 and Japanese Patent Application Kokai (Laid-open) Nos. 54-36171, 59-203239, 60-38730, 59-172159 and 61-39919, the lubricant is fixed to the surface of a magnetic disk by chemical reaction. Consequently, the lubricant is hard to disengage from the sliding surface and a considerable improvement in the durability is expectable. However, it is hard to conduct the reaction and also to obtain a homogeneous film as a reaction product. Thus, it is quite hard to use these procedures in actual practice. Furthermore, the fluorine chains are too short. For example, with a chain length of less than 12 carbon atoms, a good lubricating effect cannot be obtained, and the durability of the magnetic recording medium is not satisfactorily improved. The conventional fluorine-based surfactants and lubricants do not greatly improve the durability of a magnetic disk and it is less practical to chemically bond a fluorine-based lubricant to the surface.